Calcium sulphoaluminate cement used as mineral accelerator to improve the property of Portland cement at sub-zero temperature

To avoid the harmful effect of inorganic salt antifreeze admixture on concrete in winter construction, high early strength calcium sulphoaluminite cement (CSA) used as the mineral accelerator was added in Portland cement (PC). The effects of CSA content and pre-curing time on the compressive strength, setting time, freezing point and frozen water, hydration heat, hydration products, and pore structures and microstructure were investigated. The results showed that the compressive strength of PC at sub-zero temperature was enhanced about 300% by the addition of CSA at appropriate dosage and pre-curing time (5 wt % CSA with 2 h pre-curing and 20 wt % without pre-curing). The freezing point and the amount of frozen water of paste were decreased by the addition of CSA and pre-curing. In addition, the hydration process, hydration products, and the microstructures were significantly affected by the amount of CSA and pre-curing time.